Helicopter certification regulations require the anti-torque tail rotor to be protected so as to avoid said tail rotor impacting against the ground in the event of the helicopter taking on a nose-up position close to the ground.
For example, when landing in auto-rotation, the pilot causes the helicopter nose to take a nose-up position close to the ground, by implementing a so-called “flare” procedure. Consequently, the tail rotor runs the risk of coming into contact with the ground, which might lead to a catastrophic situation.
Furthermore, when landing at high speed, the pilot raises the nose of the helicopter strongly in order to brake.
Thus, aircraft, and in particular helicopters, advantageously include protection against impacting with the ground in the event of the aircraft having a nose-up attitude.
For example, it is possible to place a small wheel at the rear of the aircraft. Optionally, and in accordance with document EP 0 781 224, it is possible to associate the wheel with a ski.
According to document GB 357476, wheeled landing gear may be replaced by skis.
Another known device comprises a crushable and replaceable shoe arranged in a structural element. For example, the Applicant's helicopter known under the trademark Gazelle® is provided with such a shoe inside the keel of its ducted tail rotor, i.e. inside the bottom structural element of said ducted tail rotor that faces the ground when the helicopter is standing on the ground.
Nevertheless, such a shoe needs to be changed or repaired each time it makes damaging contact with the ground. Repairs are sometimes made by the owner of the rotorcraft and might take place under poor conditions.
Alternatively, other aircraft are provided with a resilient tail skid provided with at least one contact blade, a first end of the skid being provided with a curved portion.
In one embodiment, the second end of the blade is fastened by two distinct fastener means to the structural element that is to be protected. Document FR 2 554 210 shows a tail skid of that type arranged on the tail boom of a helicopter.
The skid is then cantilevered out, which is why it is sometimes referred to simply as a “cantilever”.
Skids are difficult to develop. Thus, skids need to be stiff enough for the pilot to be aware that the skid has made contact with the ground, while being sufficiently flexible to absorb the energy that results from said contact without giving rise to excessive levels of force in the structure. In spite of that difficulty, they are in widespread use on aircraft.
The state of the art also includes documents GB 462963 and U.S. Pat. No. 4,196,878, in particular.